Polyolefins are very important items of commerce, large quantities of various grades of these polymers being produced annually for a large number of uses, such as packaging films, elastomers and moldings. There are many different methods for making such polymers, including many used commercially, such as free radical polymerization, and many so-called coordination catalysts such as Ziegler-Natta-type and metallocene-type catalysts. Each of these catalyst systems has its advantages and disadvantages, including cost of the polymerization and the particular monomers (co) polymerized, and structure of the polyolefin produced. Due to the importance of polyolefins, new catalyst systems, which are economical and/or produce new types of polyolefins are constantly being sought.
U. Klabunde, et al., J. Mol. Cat., vol. 41, p. 123-134 (1987) describes the polymerization of ethylene with nickel complex catalysts having certain phosphorous-oxygen ligands. The catalysts and processes of this reference are different than those of the present invention.
U. Muller, et al., Angew. Chem. Int. Ed. Eng., vol. 28, p. 1011-1013 report on the interaction of Ni(COD)2 (COD is cyclooctadiene), ethylene and a phosphorous-oxygen compound which may be a ligand. There is no evidence for polymerization.
K. A. Ostoja Starzewski, et al., Angew. Chem., Intl. Ed. Engl., vol. 26, p. 63 (1987) reports on the polymerization of ethylene using certain phosphorous-oxygen ylides and Ni(COD)2. Ylides are not used herein.
W. Keim, Angew. Chem. Int. Ed. Enql., vol. 22, p. 503 (1983) reports the use of nickel complexes of certain arsenic-oxygen compounds to oligomerize ethylene. Higher molecular weight polymers are not reported.
P. Braunstein, et al., J. Chem. Soc., Dalton Trans., 1996, p. 3571-3574 report that nickel complexes of certain phosphorous-nitrogen compounds oligomerize ethylene to low molecular weight olefins. Higher molecular weight polymers are not reported.
U.S. Pat. Nos. 5,714,556, 6,060,569, 6,174,975 and S. D. Ittel, et al., Chem. Rev., vol. 100, p. 1169-1203 (2000) (and references therein), report the use of transition metal complexes of various phosphorous-containing ligands as catalysts for olefin polymerizations. The catalysts and processes of these references are different than those of the present invention.
One of the advantages of some late transition metal catalysts is that they can incorporate polar comonomers, for example olefinic esters, in copolymerizations with hydrocarbon olefins, especially ethylene. Palladium complexes are particularly noted for this ability, while nickel complexes often do not copolymerize polar comonomers or do so only very poorly, see for example U.S. Pat. No. 5,866,663.
It has also been discovered that using relatively high temperatures and high hydrocarbon olefin (ethylene) pressures often improves the incorporation of the polar comonomer in the polymer formed as well as increasing the productivity of the polymerization catalyst. This is surprising in view of the observations in the literature that increasing temperatures usually decrease the productivity of many nickel polymerization catalysts; see for instance U.S. Pat. No. 6,127,497 and WO00/50470.
JP-A-11292918 reports the copolymerization of methyl acrylate and ethylene using certain nickel complexes as polymerization catalysts. These polymerization are carried out at low temperatures and pressures, and mostly the incorporation of methyl acrylate is reported to be very low, and the polymers have low branching levels.
A. Michalak, et al., Organometallics, vol. 20, p. 1521-1532 (2001) conclude that, using computational methods, nickel complexes having neutral bidentate ligands such as a-dimines should not copolymerize ethylene and polar comonomers such as methyl acrylate.
Other references of interest concerning transition metal complexes and/or their use as polymerization catalysts are Keim, Organometallics, vol. 2, p. 594 (1983); I. Hirose, et al., J. Mol. Cat., vol. 73, p. 271 (1992); and R. Soula, et al., Macromolecules, vol. 34, p. 2438-2442. None of the complexes or processes with them is claimed herein.
Other references of interest concerning polar copolymers include U.S. Pat. Nos. 3,481,908, 3,278,495 and M. M. Marques, et al., Poly. Int., 50, 579-587 (2001).
All of the above publications are incorporated by reference herein for all purposes as if fully set forth.